Coating, particularly for manufacture of abrasives



March 20, 1945. R. P. cARLToN Erm. 2,371,605

Z2 Z6 Z5@ 25 25A March 20, 1945- 4 R. P. CARLTON 15T-Al.l

CQATING, PATICULARLY FOR MANUFACTURE 0F ABRASIVES original FiledA June1, 193s 5 sheets-sheet 2 fr. \s

RLTON ET AL March 20, 1945. R, P, cA

, COATING, PARTICULARLY FR MANUFACTURE OF ABRASIVES nz Jaa/rg..

March 20, 1945. 2,371,605 coATING, PARTICULARLY FOR MANUFAGTURE 0FABRAsIvEs R. P. CARLTON Erm.l

originai Filed June -1, 193s 5 Sheets-Sheet 4 COATING, PARTICULARLY FORMANUFCTURE- 'ABRAS IvEs original Filed June 1, 1953 `5' sheets-sheet 5IPatented Mari 20, 19.45 l

COATING, FOR MANUFAC- TUBE F ABRASIVES Richard Paul Carlton and TheodoreJoseph Miller, St. Paul, Minn., assignors to Minnesota Min`` ingit'Manufacturingr Company, St.-Paul, Minn., a corporation of Delawareoriginal application June 1, 1933, serial No. 673,886. Divided and thisapplication March 31,4938, serial No. :tasso This application is adivision of our copendlng application, Serial No. 673,886, filed June 1,1933.-

This invention relates broadly to coating and coating materialsespecially in sheet form, such voids in the wheel acting as clearancesfor the s claims; (ci. 117-17) material being abraded be provided sothat fast and continuous cutting, together with reduction in temperatureof the wheel when engaging the work, should be attained. In obtainingthese deas in th'e manufacture of abrasives, and the pres- 5 siderata itis found that the porosity of the wheel ent invention among other thingsfinds utility in in the case of a molded structure tends to weaken oneof its phases in the manufacture of abrasive the disc or wheel and, dueto the porosity, the wheels or discs, and while the invention in one ofstructure does not have suicient bond to firmly its forms is illustratedas adapted for coating and anchor the grit therein. forming an abrasivedisc, it will be understood l0 The principal'objects and advantages Yofthe that certain other phases of the invention are of present inventionreside in the provision of an quite general application and may beadapted for improved method of manufacturing an abrasive other purposes,such, for example, as a nmethod wheel, disc or the like havingcharacteristics in its of coating roofing material with pulverulentminstructure which increase. the cutting ability, eral. l5 ystrength anddurability of the device; the provivThis invention, aswili hereinafterappear, nds sion of an improved method of manufacturing an especialutility in the production of grinding discs abrasive article such as awheel or disc for abradwherein the abrading surface is on a sidethereing purposes, in which the cost of manufacture of rather than onthe periphery; and the invenis" considerably reduced, with the attendantaction also finds utility in coating roofing material complishment ofthe desired control of ratio or so that particles of mineral depositedthereon are bond, that is to say, adhesive, to the mineral or caused tolie ilat, that is to say, `with their major grit, and -to provide suchan improved method in dimensions Vsubstantially parallel -With thesurwhich the same may be carried out as a substanface of the backing.tially continuous process, thus simplifying the The customary proceduregenerally resorted to manufacture and reducing the ultimate costs; thein the manufacture of abrasive wheels, discs and provision of animproved method of manufacturthe like generally includes the mixing ofan abraingabrasive wheels and discs in which a fabric sive grit, such asaluminum oxide, silicon carbide such as paper, cloth or the like may beemployed or emery, with a suitable bonding material and as a carrier forthe bond and4 grit and in which then placing the mixture in a mold. Thefinal the ultimate size of the abrading wheel or disc setting up of thebonding material is then eected may be determined easily and by asubstantially by curing at a sufficient temperature to cause thecontinuous method; the provision of an improved bond to iiow and take afirm grip of the abrasive form of abrading wheel or disc wherein acongrit. Several different forms-of the adhesive or trolled porosity ofthe structure is obtained and bondingmaterial are used, the more commonbe 35 wherein the ratio of adhesive material to grit is ing that knownas a vltriiied or ceramic bond.. In substantially uniform throughout theentire making such a wheel it is necessary to fire the.l wheel or disc;the provision of an improved abwheel, that is to say, subjectl themixture of bond- 4rasive article such as a wheel or disc wherein the ingmaterial and grit to a sufficiently high tem- J gritparticles areoriented so that their most perature to cause the bonding material toflow effective cutting edges are presented at theV and thus, in effect,form a porcelain bond be` abrading surface and thus are brought intocontween the various particles of grit. Obviously, tact with the workmore eiiiciently; the provision such a wheel or disc is infierribie,broadly, and will of an improved method of manufacturing abranot standshock or sudden thrusts. sive discs,` wheels and the like in which thepro- It has been proposed to employ as substitute duction of theabrasive article may be carried out bonds for the vitried or ceramicbond, materials on existing sandpaper type of equipment, with such asrubber, shellac, sodium silicate, naturalv the subsequent'convenience ofshortening .the and synthetic resins and the'like. y required time forproducing various sizes of ab- In producing an abrasive disc or wheel,aside rasive wheels and discs. from the problems of choice vof bond,there is also lil) A further advantage of this invention residesin thenecessity of controlling the ratio'of bonding that, as distinguishedfrom the molding process material to abrasive material, and it is alsohighly' of making abrasive discs and wheels, which redesirable that, incertain forms of the abrasive quires-that the abrasive grit and bondingmawheel or disc structure, more or less porosity or terial be mixed inthe proper ratio, then molded,

then heated, and therefore requiring each sepa- A vention permits of thecarrying out of a substantially continuous process similar to themanufacture of sandpaper and that continuous lengths of the material maybe stored in drums or rolls from which the desired widthl of strip maybe cut which is to determinethe ultimate thickness of the wheel, itbeing assured atall times that the ratio of abrasive material .tobonding material will remain substantially uniform throughout theparticular wheel or disc structure which it is desired to form.

The present invention also permits of the manufacture of the basicabrasive material on standard sandpaper equipment and that this materialmay, after having been prepared, be preserved in stabilized form for usein-manufacturing wheels as desired, the process and the article thuspermitting of the production of one or more wheels of'l a desired sizeand texture, that is to say, gritsize or number, at less cost and moreconveniently than is possible with the previous/processes known to us.

It has also been suggested in the prior art that one of its objects theimproved method of and apparatus for subjecting the abrasive grainsduring the flight by gravity to the sheet to the effect of an electricaleld, preferably of the electrostatic type, for aligning the particleswith the lines of force of the eld, which for convenience liesubstantially parallel with the surface of the abrasive sheet, thusorienting the grains in the proper desired manner as they are depositedthereon.

This invention also contemplates the improved method of incorporatingthe grit particles in an adhesive in plastic form, and while the same isdeposited together with the grit on a ilexible backing subjecting theincorporated grit and 'adhesive to the action of an electrical field foralignabrasive discs and wheels be made up of a series.

of superposed discs of ordinary sandpaper, emery paper or cloth or thelike glued together and subjected to pressure and heat, but in suchprior A process and articles made therefrom known to meconsiderable'waste occurs in that 'the discs must be cut from a standardmade piece of sandpaper, and the portion thus made and not used must bethrown away. The present invention distinguishes from such process inthat there is substantially no waste of abrasive material which isattendant upon any dieing out process, hitherto suggested.

The present invention also has' as one of its objects the provision ofan improved method of producing a iiexible abrasive article and theresultant article so that, as desired, the manufacturer may produce anabrasive article of the desired degree of flexibility, and, at the sametime, have a substantially homogeneous structure with a substantiallycontinuous abrading surface.

The present invention also contemplates the employment therein and forthe production of the abrasive article of a new process of orienting theabrasive grains so that vtheir sharper points will be presented at theabr'ading surface. In ordinary sandpaper the abrasive grains aredeposited on the adhesive coated sheet by gravity and as a result lie inhaphazard fashion in the adhesive. I

In the present invention it is desirable that the` abrasive grains beoriented so as to present the longitudinal axes of the individualparticles in a position substantially parallel with the plane of thesheet and substantially perpendicular to the margins thereof so thatwhen the abrasive article is-Lormed from a sheet of abrasive materialmade; according to this invention, .to form an abrasive disc, thesharperpoints of the grains will be presen d attire margins at each of theconvolutions of he disci` This orientation of the grains may beconveniently aiornplished by the action of an electrical ileld, and itis therefore one of the further obJects of thisinvention to provide animproved method ofand apparatus for subjecting the abrasive grainsto theaction of an electrical field for the purpose of attaining thedesiredorientation of such particles; the invention further has as slit to anydesired width which is to be the depth ing the particles and orientingthe same in the desired manner. x

The method involved in the present invention may lbe carried out in anumber of alternative steps, depending upon 'the form andcharacteristics as to flexibility and denseness which it is desired toimpart to the finished article.

A preferred method of producing the abrasive article of this inventionincludes the selection of a fabric, preferably paper, of a desired andsuitable weight, coating this paper with a bonding material and asuitable grit. For our purposes, we prefer to employ'a waterproof bond,and, for example, this may be any of the bonds described and claimed inthe patents to Okie 1,565,027, 1,565,028, 1,635,801, Carlton 1,775,631,1,736,964.

This paper thus coated with a waterproof bond and a suitable grit may beof the same characteristics as the waterproof sandpaper now known to thetrade as Wetordry."

The coated fabric, preferably paper, having th grit contained in theadhesive layer may be provided with a light-or heavy sizing coat,depending on the use to which the material is to be applied,

though in most instances a sizing coat may be ilcient period of time todry or partially solidify the adhesive. It is preferable that theadhesive be not set to its final condition at this time but to aid inhandling the adhesive should be dried 'to a degree which will preventaccidental displacement'.l of the grit.

'I'he abrasive sheet thus formed may be rolled into what are known asjumbo rolls and may be stored -until required for slitting into suitablewidths. When it is desired to complete a grinding disc with thismaterial the same may be of the disc or wheel-and then' wound into rollsof the required diameter. Owing to the fact that the vadhesive materialis not entirely set when the sheet is wound into a roll, the disc orwheel thus formed may .be placed in an oven for further drying and forcompletely setting up the bond.

By regulating the tension of the strip of abrasive material as it iswound into disc-like form vflexibility of the articlemay beregulated. Asto the waterproof qualities of the article, excellent resultsmay beobtained by' employing any of the' binders disclosed inthe patentsmentionedherein.

article we thus are able to produce an abrading surface which hassufficient flexibility as to bind er and composite to facilitate surfacesanding, as it is called, and also to facilitate clearing of the wheelwhen it is in use.

We have found that in some cases of flexible discs or wheels it vmaybe'desirable to cement the layers or convolutions of the disc together,but this is not the preferred practice for the normal surface sandingjob, and we have found that for such purposes merely winding the stripof material upon itselfl and then attaching it to a suitable backing,preferably flexible in nature, will produce a grinding wheel or discgiving a desirable flexibility and an efllcient cutting surface.

In instances where it is desired to make a solid wheel, that is, arelatively inflexible wheel or disc,

I it may be desirable to cement the laminations,

layers or convolutions, as they may' be termed and this may beaccomplished byinterposing a sizing coat as the strip is wound into thedisc form. It also may beudesirable in some instances to apply thesizing material in a relatively heavyI This operation may also beaccomplished when the disc is wound by immersing the same in a bath ofadhesive size to permit the adhesive material to flow of'capillaryaction between the 1aminations or convolutions of the disc.

One of the important factors which effect flexibility when the disc isnot `of the solid type is the degree of tightness of winding, and thusby relatively loosely winding the strip of adhesive material it ispossible ultimately to obtain a very flexible abrasive disc. I

It is important in the production of a grinding or polishing disc orwheel of the character herein disclosed 'that the ratiol of mineral gritto adhesive be controlled to produce the most desirable coating resultsand also that the uniformity of this ratio throughout the disc bemaintained. By the abrasive article of this invention and the method ofmanufacturing the same, we are enabled to attain a high degree ofefficiency in cutting operations of the disc and to give to the abrasivearticle a substantially uniform effective abrasive surface throughout,so that as the same becomes worn in service it yet renders the sameeicient cutting and/or abra-ding or polishing functions.

It will be understood, of course that dependent upon the desiredcharacteristics of the finished product, we may employ fine, medium orcoarse grits and that, correspondingly, the thickness of paper or otherfabric employed and the' ratio of adhesive to grit or abrasive particlesmust be controlled in each instance to the desired degree.. In certaininstances We applied the adhesive and abrasive coatings to both sides ofthe backing.

In selecting an adhesive material,v we have obtained excellent resultswith adhesives formed as composite materials f-rom Bakelite, that is,phenol and formaldehyde and-other synthetic resin binders, rubber,shellac and the like, it being understood that these materials may bemade into a liquidA adhesive and can be further molded or softened bysubsequent flowing under heat in such manner that a thorough setting orcuring of the adhesive is accomplished without detracting from theflexibility thereof.

One example of an adhesive which is suitable for our purpose is thatsubstantially according to the following formula:

Parts Bakelite resin `4 Thinner (denatured alcohol) 1 produced. Thisadhesive is then applied to th sheet which then receives the abrasivematerial.

In the case of a Bakelite resinous material, the adhesive is dried afterhaving received the mineral either on -the racks or festoons or at someother point in the production of the abrasive strip, and we prefer toemploy temperatures ranging from normal atmospheric room temperature toapproximately degrees Fahrenheit, depending on the'length of time ofdrying. In this drying operation the temperature is maintained at such apointthat the thinner or solvent only will be driven off and thus noappreciable hardening or solidifying reaction takes place in the resinat this time. When the strips are coatl ed with this material togetherwith a binder, heat treated as set'out above and then wound into discsor wheels, they may be further subjected to heat which causes a flowingof the resinous binder and thus sufficiently unites the severalconvolutions or laminations of the wheel. Of course, if it is desired tomake a substantially rigid Wheel in this manner, same may be' tightlywound and l also subjected to pressure as Well as heat subsequently.

When employing a synthetic resinous material such as a Bakelite resin,the same is thinned with practicable. The thinners are evaporated atnormal temperatures, and the bond thereupon solidies to the consistencyof but tack free.

.Tle abrasive article in this condition may `then be stored in largerolls and cut or slit into ribbon disc portions as required.

In order to insure flexibility of the abrasive article during handling,it is preferred that the rolls be stored in a humid atmosphere, so thatthe article will be possessed of flexibility during the heatingoperation.

After the abrasive material is cut and formed into ribbon discs, thebond may be toughened by further heat treatment at, say, to 185 `degreesFahrenheit for approximately fifteen minutes, which produces a flexibleconsistency and is suitable for some purposes, or, we may employtemperatures ranging from 250 to 300 degrees Fahrenheit fora period oftime of from fifteen minutes to one hour to produce a relatively hardbond in which there is substantially no flexibility in the binder coatitself. Where a flexible binding coat is desired. a proper regulationofthe temperatures and employment of suitable modifiers in the Bakeliteresin will give satisfactory results.

It will be understood that the preference to storing the abrasive inlarge rolls, jumbo rolls, as

they are called,is that sometimes it is dimcult to synchronize theheating operation with the avarnish partially dried drying festoons, andfor some purposes it is preferred that the abrasive sheet as it isformed be placed in jumbo rolls so that it may be slit to the desiredwidths as required.

In connection with the foregoing formula we have secured a flexibleabrasive strip to be wound into a disc or Wheel shape by employing aBakelite material which doesy not produce a complete reaction torigidity' or by keeping the temperature below 212 F. and reducing thetime of heat treatment.

For the purposes of this invention we prefer` to employ a flexiblebinding material on the flexible backing, but it is to be understoodthat a satisfactory flexible Wheel or disc may be produced employing arelatively less fiexible binder by keeping the layers or laminations ofthe wheel separated.

We have made satisfactory abrasive wheels or discs by employing anadhesive of the varnish type such as is disclosed in the patents to Okiehereinabove referred to, and we have also employed as a binder thematerial disclosed in the application of Carlton and Oakes, S. N.660,319.

Where rubber, shellac or synthetic resins other than Bakelite areemployed, we also prefer to qheat treat the same in the final settingor, if necess of making the sheet simultaneously with the application ofthe adhesive and grit.

The outstanding advantages of the present ininto a roll to form a discor wheel, reside in that we are enabled to produce a laminated abrasivestructure in which the abrading surface presents a more definite andmore uniform porosity due to the laminations and due to the spotcontacting of the adhesive on one layer with the adjacent layer, andthus producing a greater proportion of voids than is possible orobtainable where abrasive grit 'and a bond are molded even where equalratios of bond to grit are employed. O ur .invention also produces alaminated abrasive structure having an increased strength due to theincorporation therein of the coated backing of fabric such as paper .orcloth, which adds to the strength of the entire wheel making the sameless brittle and more flexible and permitting of y ,thinner wheels to beprepared than by any other prior method known to us.

Another distinct advantage of our invention resides in the fact that themineral grits, owing to their elongated nature, may be oriented on theabrading device so thattheir sharp points are presented at the abradingsurface. For some purposes .it'is desirable to 'deposit the abrasivegrit by an electrical eld or other electrical action, such as by anelectrostatic field, in such a manner that the grits will becomeoriented with their major axes parallel to the surface of the sheet andperpendicular to the abrading surface, particularlywhere the grits areplaced so that their major axes are perpendicular to the marginsI of Ithe strip from which the wheel is wound. We

shall describe s uch a process of deposition of the grits more fullyhereinafter.

It will be understood, ofl course. that after the abrasive strip hasbeen wound to the desired diameter and with the desired degree oftightness. a suitable disc backing may be'afiixed by a waterproof binderif desired on one surface of the resultant abrasive disc so that thedisc may be mounted on a suitable shaft for impartingrotation thereto. A

The several methods which may be employed in the manufacture of theabrasive article itself are illustrated in the accompanying drawings, inWhich- Figure llis a schematic view of an apparatus which may beemployed for producing the abr'asive article of this invention.

Figure 1a is a schematic view of a slitting and winding apparatus whichmay be used with the apparatus shown in Figure 1.

Figure 2` is a plan view of an abrasive disc made according to thisinvention.

Figure 3 is a transverse sectional view taken on the line 3-3 of Figure2 looking in the direction indicated by the arrows.

Figure 4 is an enlarged transverse sectional view taken on the line 3--3of vFigure 2 looking in the direction indicated by the arrows.

Figure 5 is a schematic view of apparatus for coating one or both sidesof the abrasive article.

vention, particularly where the same. is wound IFigures 6 and 7 arefragmentary sectional views of an alternative form of an abrasivearticle made according to this invention.

Figure 8 is a schematic view of an alternative form of apparatus forsecuring orientation of the abrasive particles. l

Figure 9 is a view showing the apparatus of Figure 8 from anotheraspect.

Figure 10 is an elevational schematic view i1- lustrating alternativeapparatus 'for carrying out the step of orientation of the abrasiveparticles.

Figure 11 is a perspective view of an alternative form of apparatus ofthis invention.

Figure 12 is an elevational view of a still further modii'ied fcrm ofthe invention.

Figure 13 is an enlarged sectional View of a sheet illustrating thealignment of the abrasive grains thereon.

Figures 14, 15, 16, 17, 17a, 18, 18a and 19 are all diagrammatic -viewsof alternative forms of the invention shi-own in Figures 8 and 9.

Referring now more particularly to the drawin-gs, and first to Figure 1,therg is shown a roll of fabric such as paper, or cloth 5, from whichthe web 6 is unwound over an idler roller 1, to receive from a coatingroll 8 a layer of the adhesive material delivered by the yseries of feedrolls 9 from a tank I0. The web 6 is fed beneath a hopper I I from whichis supplied a quantity of oomminuted abrasive material I2 by gravity.which may be suitably regulated in any desired manner to determine thethickness of the grit layer. The positioningvof the abrasive materialmay be controlled at this point by the use of electrical orientingapparatus as shown in Figure 8 and hereafter more fully described. Thesheet or web 6 is thentrained over'a roll I3 and reflexively bent uponitself by a roll I4, some of the aesive sumciently to permit handlingfofthe abrasive coated strip or sheet indicated at da as it'leaves thedrying room. At this point Figure l shows the sheet as broken, indicatedat i8, inasmuch as it may be desired to store the resultant product atthis point before continuing the same to the slitting apparatus. Howbeexercised thatthe proper weight of paper with regard to abrasive andadhesive be selected.

The disc-like structure thus provided may be secured to a flexiblebacking 29 of paper or cloth or other suitable material having an axialopen-- ing by which the same may lbe attached to `the rotating shaft ofa grinding machine.

ever, if it is desired to have a continuous making l From the slittingapparatus the several resultant strips of abrasive sheet material may befed to a mandrel 2 I, on whichthey may be wound into the nalabrasivedisc elements producing the articles such as shown in Figures2,'3 andv 4.

It will be understood that while the strip shown at 6b in Figures l andla is wound with the abrasive coated side outwardly, thus leaving anouter abrasive coated surfacev exposed at the last convolution, the discmayv be as readily wound in the opposite direction so that the abrasivecoated surface of each lamination will be presented inwardly. Inasmuchas these discs are intended to grind on one of their side faces, and asa substantially continuous abrasive coated surface is thus afforded, thediscs may be Wound either way desired.

It is also to be understood that by placing the strip 6b under more. orless tension as desired, a tighter or looser wound disc may be obtained.

When the abrasive `material is deposited by gravity as shown in Figure1, it will be understood that the abrasive grains Vwill be largely lyinghaphazard on the abrasive surface, though a large number of them will beoriented by the contactof the freshly coated surface with the roll I4,so that 'when the strip 6b is wound into a roll toform the disc thegrains willbe knocked down in such a manner that their sharper pointswi1l,as the disc is employed in grinding or polishing the surface. bebrought against the surface of Vthe work. However, to insure that themajority of the grits will be so oriented, we have provided methods andapparatus for so orienting the grains which will be-dbed more rullyabrasive coated material faffording a laminated abrasive structure. Thelaminations are held together by the adhesive material establishingcontact onone convolution with the back surface of the, adjacentconvolution so that av struc- It will be understood that the backing 2lshould be cemented to the disc by a flexible ,f `waterproof adhesivesimilar tothat employed in the disc itself, or, if desired for somepurposes,

the backing 29 `may be of a rigid material and the disc likewisecemented theretot In Figure 4, it will be understood, of course. thatthe thicknesses ofthe convolutions and layers of grit and adhesive havebeen greatly exaggerated in size, although it is conceivable that onemight produce an abrasive article having convolutions whose thicknessesare as great as those shown in Figure 4. However, in the or-v at 3l inFigures 2 and 3. It will also be noted that the grooves 3i areypreferably of greater depths at their inner ends toward the axis of thedisc than at their outer ends adjacent to the periphery of the disc.These grooves may be formed in the disc after the fabrication of thesame inasmuch as forming the grooves in the strip prior to nally windingwould require considera'ble care in aligning the notches in eachconvolution from which these grooves are formed. The disc thus formedcontains a number of voids which are afforded by virtue of the gritparticles themselves holding the laminations apart and by the vacantplaces indicated at 25a where the glue or other adhesive does notcompletely fill the spaces between the convolutions. I

Thus the abrasive article quickly cleans itself as it works and cloggingor loading of the article is practically impossible.

' We have found that a satisfactory grinding and polishing wheel may beconstructed by methods disclosed herein, and in one formof theinvention, which is illustrated in Figures 6 and VFigui-2. 3 mddillustrato a disc made according to this invention, wherein the disc iscomposed of s plurality of convolutions -22 of ture somewhat similar toFigure 4 will 'be obtained, the innermost .convolution 22a having itscoating 23 of adhesive material contacting at a y plurality of points,indicated at "2t-24 with the back surface 25 of the immediately4adjacent convolution` 28.*, Thus the abrasive grains indicated at 21inthe layer of adhesive 23 are substantially embedded therein with theirmaior axes and thus'their sharper cutting points presented toward themargins of the laminations. In this way a substantially continuousabrading surface indicated at, on the surface of the disc is thusprovided. k be understood that care must 7s A satisfactory 'formulawhich we have em- 7, we apply a coating of adhesive material oontainingan abrasive to both sides of the strip forming the exible abrasivearticle. This coating operation may be accomplished by the apparatusshown in Figure 5.

` After making a double coated strip, it is then wound loosely into aconfiguration substantially like that shown in Figures 6 and 7. The thuswound material is' then thoroughly cured 'and dried. After curing, thedisc-like structure then afforded is cemented to the cloth backing insuch a manner vas to preserve the open or spaced This drying time, We ndto give best results by subjecting the article to a drying temperas turefor approximately forty-eight hours.

a desired degreelof of the sheet.

ployed for the purpose of compounding the polishing material may be asfollows:

Grams Nitro base thinned to 50% solids 200v Dibutyl phthalate 4.0 400silicon carbide 40.0` Tripoli 150.0 Borax 16.0 Erkalin 4.0

From the foregoing it will be observed that we produce a convolutedstructure indicated generally at 50, composed of the laminations of theconvolutions I of suitable fabric coated on both sides as indicated at53 and 54 with adhesive B5 gntaining the comminuted abrasive materialform of the apparatus does not. however, produce orientation of the gritparticles with their maior It wm be noted vthat 'sufficient space isafforded between the layers 5I particularly as shown in Figure 7 topermit of the introduction'of a comminuted polishing material indicatedat v51. Thus aaxes paralleltothe plane ofthe sheet. and reference will-be made hereinafter to forms of the invention including apparatus forthis purpose.

It will be understood that the sheet may be coated on both sides byrunning it twice through either a gravity coating apparatus or any'ofthe apparatus shown in the other figures of the' drawings.

As herein pointed out, it is desirable to orient the grit particles sothat they will lie with their .major axes substantially parallel to thesurface to -be coated, and they will thus present their sharp points atthe edges of the strip as the same becomes worn in` use as an abradingdisc.

This orientationof the particles uniformly on the sheet is also ofutility in the manufacture v Wmie orientation of the gras' with theirmajor axes parallel with the surface of the sheet and substantiallyperpendicularto the edges thereof. may be more or less accomplished insimple gravity depositionof the lgrits on the adhesive coated sheet, apositive orientation of the individual grains may be accomplished byelectrical action. that is to say, the grits may be deposited on thesheet in the presence of an electrical field, for example electrostatic,or if the gritparticles are .of'a 'magnetically responsive nature thenin the presence of an electro-magnetic eld.. Grits deposited in thepresence of such an electrical iield will be caused to align themselveswith the lines of force of the electro-magnetic .or electrostatic eldas. the case may be.

g For most abrasive articles an electrostatic nein will perform themction inasmuch as most of the grit particles commonly employed in theabrasive arts are of a non-magnetic character. and are non-conductorsand practically all will respond to the force of an electrostatic eld.

Referring' specifically-tovFigure 5, we provide a suitable 'backing forcarrier strip 83 which receives coats of. adhesive material on bothsides thereof from a suitable tank 64. the strip being conductedupwardly between two chambers 65 and 66 and then conducted through edgeguide rollers 01. H

In the chambers 55 and'BS there are'provided kelectrodes 68 and' 69 ofpreferably negative polarity, the sheet being itself of a conductivenature and connected to the positive 'side of a source of velectricmotive force indicated at'10.. v

The apparatus receives grit from hopper-s 1| and 12 which' is agitatedin the form oficlouds within the chambers 65 and 66 by air blastsintroduced at the nozzles 13 and 14.'-

The apparatus shown in Figure is similar to I that shown in the patentto Smyser 1,788,600,

of mineral coated shingles wherein it is desirable that the particles ofmineral, granules or thelike, be deposited so that a minimum number ofthe mineral granules is required to cover a given area of the asphaltumsheet or other material from l)which the carrier or backing of theshingle is made.

We have illustrated herein a number of ways in which this may beaccomplished which are all included in the disclosures of Figures 8 to12, both inclusive, and Figures 14 to 18, both inclusive, it beingunderstood 'that these electrical orienting devices are to be vusedfinthe general apparatus shown in Figures 1 and laat the point indicated bythe hopper Il.

' With reference-rstto Figures 8 and 9, we have employed a backing '16.of'suitable material which receives a coating on the upper surface ofthe horizontal flight thereof shown in Figure 8, this coating beingapplied from a set I2 and 83, between which the horizontal ight ofadhesive 'distributing or applying rollers 11, 18 and 19, the lattertaking up adhesive from a tank 80. This adhesive layer is indicated at8l and the backing is then propelled to the left as viewed in Figure 8between electrodes forming an electrostatic field.

These electrodes, we have found, may conveniently comprise a pair ofcircular disc-like plates f of paper 16 passes at a desired rate ofspeed.

Other forms of the plate electrodes may be employed, but we have foundthat this type produces a uniform field and highly satisfactoryperformance.

Above the flight 18, and at a distance suiiiciently remote from theelectrodes so as to be substantially unaffected thereby. we provide ahopper 84. which may contain vabrasive grains of the desired size. Wefind thatfor our apparatus an abrasive grain or pulvule of a sliverycharacter that is sonewhat elongated, will give highly desirable resultsas to orientation, though it will be understood that it is notnecessary'l that-this type of pulverulent material be employed in orderto attain the results of this invention. .Prac. .tically allof thegritsemployed'in theabrasive industry-today are'characterized by havinga major and a minor axis so that they 4become responsive to the actionof an electrical neld and serves to illustrate one apparatus forcarrying out the double coating simultaneously. This lwhen introducedinto the presence ofthe same.

These grits are deposited by. gravity from a hopper '84 having asuitable controlling gate 85 over a distributing roller l0. so that theyfall in a substantially continuous stream 81 toward the adhesive surfacell.. passing between'the electrades 92 and @3 in their path to theadhesive surface. I

We have discovered that a static electrical field solely, that is tosay, without outside inuence, mechanical or otherwise, acting upon thegrit particles, tends to deflect them toward one of the plates, and inorder to correct this and produceV a more uniform distribution and yetobtain orientation, we employ a pole changer, diagrammaticallyillustrated in Figure` 9, through which the two electrodes 82 and 83 areconnected to the source of electrical difference of potential.

A source of electromotive force, preferably of relatively high voltage,is provided. The `voltage employed in one arrangement of the electrodeswas about 105 kilovolts and in employing this voltage the platesorelectrodes were spaced about 5.5 inches apart in air. This arrangementserved to maintain a constant electrical potential gradient ofapproximately v19 kilovolts per inch between the electrodes.

In correcting for uneven distribution, the electrical center of thesource of difference of potenf l tial is grounded as indicated at 83a inFigure 9,

and the source` composed of two units 85a and 86a. is so connectedthrough pole changing switches 81a, 88, 89 and 90 that the relativepolarity of the two plates 82 and 83 forming the electrostatic ield waschanged at a desired frequency.

We have found that, for our purposes, with.

the plates spaced between and 6 inches apart in air, the best resultsare obtained by the use of electrical potential gradients of the rangeof from 1'1 to 20 k. v. per. inch. We also find that where reversal ofpolarity is resorted to, as in the disclosure in Figure 9, the optimumof frequency of polarity change or reversal should' be inthe vicinity oftwo cycles per second. How-` In the more convenient form of theinvention shown in Figure 9, successful results will be obtained byemploying disc-like electrodes 82 and 83 of a diameter of about 8inches, `and with the opposed faces of the electrodes substantiallyparallel to each other.

A further form of apparatus which we may employ for carrying out thismethod of deposition is illustrated in Figure 10 wherein the strip,sheet or web of Figure 1 is indicated at 33,`the one side of said sheetbeing provided with a layer 34 of adhesive material, preferablywaterproof in its characteristics, though, as will-be obvious, thislayer of adhesive may be of the ordinary blue bond type employed in thesandpaper industry for non-waterproof abrasive articles. l

The sheet 3'3 is caused to travel in a substantially horizontal planebelow a hopper 35 and between the electrodes 36 and 3l of an electricalfield, the electrodes 36 and 3l being connected to an appropriate sourceof electrical potential of the required value. .In actual practice whatare known as high voltages may be required, though it will be understoodthat the diierence of potential to be employed is subject to variationas desired for accomplishing the ultimate desired action.

For the purpose of the present disclosure the electrodes 36 and 31 formpart of an electrostatic field, that is to say, a field in which aconstant stress is set up but in which relatively small currents flow.Such an electrical eld will be established between the electrodes 3G and31 indicated generally by the lines of force 38.` This eld is set upbetween the electrodes 36 and 3l above the sheet 33 and below the hopper35, and the field strength is regulated to such an extent as to act uponthe abrasive particles as they are fed from the hopper 35. j

Thev abrasive particles are shown as a cloud 38 but some of them areshown enlarged at 40 depicting the approximate positions which theyassume as theyfall by gravity through the elecv trostatic field. It willbe understood thatshould change, and size of and distance between theplates is all subject to variation to suit the particular conditions andresults to be attained thereby.

'We have also found that with diierent types of abrasive grainsdifferent results were obtained.

sol

For example, with silicon-carbide in some arrangements of the'platescompensation had to be e for difficulty encountered due to the highconductivity of silicon carbide, where as with certain other gritparticles these diiculties were not found present, such, for example, asin theuse of flint.

From the foregoing it will be understood vthat the electrostatic fleldestablished either constantly or intermittently ltogether with reversalof polarity between the plates 82 and 83 aects the grit particles, asthey enter the electrical ileld,

electrodes and the backing itself. this diiilculty iinreliminated bytheform of the electrodes,

so that the major value and resultant force of the electrical field isretained.

charged electrode and they will fall upon the l the electrostatic eld beof great enough strength, the particles issuing from the right hand endas shown ,in Figure l0, would be cause to orient themselves with theirmajor axes parallel with the lines of force of the electrostatic eld andbe projected byr that field from one of the electrades toward the otherthereof.' ,Therefore by regulating the electrostatic field to thedesired optimum the particles will be caused merely to flatten out, andwhile theymay, under these circumstances be caused to travel along thelines of force of the field, the force of gravity will tend to overcometheir flight toward the oppositely layer of adhesive, assuming positionssubstan- .tially as shown in Figure 10, and indicated at Il.

This orientation is more uniformly accomplished, however, in the form ofthe apparatus shown in Figures-8 and 9. I

Inasmuch as the particles of abrasive material asthey leave the hopperadjacent to the electrode 36, may in a large number ofA instances neverreach the sheet, due to their attraction to the other electrode,` weprovide a movable partition in the hopper, which may be adjustedtransversely of the longitudinal axis of the sheet so that the length ofthe slot in the, bottom of the hopper may be varied to cause the gritparticles to issue through only a portion'vo'f saidslot. A suitablehandle properly insulated indicated at 43 may be employedforreciprocating 4the paration 42 end for adjusting seme tothe desiredposition.

In some instances the particles of grit will take on charges which maytend to cause them to induce a charge in the sheet and thus theparticles would land on the sheet substantially perpendicular to theplane of said sheet. In order to avoid this as much as possible and tocounteract a tendency for the particles to assume positionsperpendicular to the sheet, the electrodes 1o 36 and 31 may besupplemented by auxiliary electrodes 44 and 45 which may have ayoltageregulated (by means not shown) to exert a sufiicient electrostatic iieldeffect or action to prethe mass is subjected to the force of an elec-Atrostatic field l2 set up between the electrodes 60 and 6l thusorienting the particles of grit contained in thexadhesive according totheir elec- 'trical responsiveness to su-ch a. eld, that is to say, thegrits having major and minor axes, as hereinbefore pointed out, willunder the influence of the electrostatic field become aligned with thelines pf force 62 shown in Figure 12, while in the glue or otheradhesive and thus be carried by the glue or adhesive on to the sheetvent the particles from taking undesirable posi-i tions just as theystrike the glue. If desired, this auxiliary field whoseY lines of forceare indicated at I6, may be extended a desired distance beyond the pointof actual deposition so that it will func-` tion for a'period of timeafter the sheet has '20 moved beyond the effect of the major electro-lstaticeld. f

Inasmiich as the poles or electrodes 36 and M and 31. and are of likesigns, there will be no tendency to set up extraneous electrostaticfields between these electrodes other than substantially ineffectiveelectrostatic or electro-magnetic elds, as the case may be, due todifference in actual potential of the two fields 38 and 46. In any Yited thereon.

event, inasmuch as the electrostatic iields em- 30 ployed have theirlines of force substantially parallel, the effect of -any extraneousfield set up betweenA the electrodes 36 and and 31 and 46 should besubstantially negligible in disturbing In order to make clear to thoseskilled in the art the basic principles involved in employing theelectrostatic ileld^`for the purposes of the present invention, Figures14 to 18 have been incorporated in this disclosure showing the varioussteps in development to obtain the optimum of results in deposition,distribution and orien tation oi therabrasive particles.

It will be understood that these Figures 14 to 1s auulustrete methodsfor producing deposithe desireddeposition and orientation ofthe par- 35ticles on the sheet'.

An illustration of one arrangement of the electrodes which will set upthe desired electrical action is shown in Figure `11 in perspective. Of

course in some instances it may be desired to n eliminate the secondaryelectrostatic eld I6 and by proper control of the moving partition I2the desired results may be attained as to ultimate effect of the fieldon the grit particles.

Figure 11 serves to illustrate a further modied form of the hopper. Inthis form the hopper is of a general V-shape cross section and thebottom thereof being open is provided with a tapering -slot indicated at41. The slot is of greater i dimensions at one end than at the other endso that by proper positioning of the hopper the particles of abrasiveacted upon by one of 'the' `electrodes and tending to be projectedi'fcbwd, the other thereof would be counteracted by the tapering slot inthe hopper, thus preventing pi1- 4iixg up of the abrasive grit at onemargin of the s ee It will. also be understood that by regulating theheight of the hopper 46a from the sheet that different effects may beobtained to the point where the desired orientation and deposition ofthe grit is attained.

The electrodes '4K4 and 45 may be 'employed in' i Figure 11 as inFigure, 10 ii"I that be found necessary under the circumstances.

Referring now to Figure 12. the apparatus. here shown discloses ahopper' 58 intowhich the comminuted abrasive material and anadhesiviematerial in plastic form are introduced. 'The tion,distribution and orientation, but that some produce better results thanothers as will appear from the following description.

On reference to Figure 14, a pair of electrodes, preferably in the formof circular discs 92 and 83 are employed, one -of these discs beingconnected to the positive side, such as at 94,- of a source ofdifference of electrical potential and the other disc being connected tothe negative side or ground as the case may be.

A relatively high difference of electrical potential was thus impressedon the two plates establishing an electrostatic field between them, intowhich-abrasive particles 8O were., introduced,

either by gravity asshown in Figure 14, or by any other suitable means,so` as to produce a stream of the particles as theyenter theelectrostatic field established between the plates 82 and 93.

Thispair of substantially circular metal plates v are made about 8inches in diameter and provided with .curved edges indicated `at 91 and98, thus preventing excessive concentration of the eld at the edges ofthe plates thereby reducing the possibility of sparking between theplates.

These electrode plates were spaced about 5.5 inches apart in/ air andwere connected to a source of electromotive force approximately ..105

'kilovolta so that a substantially constant electrical potential rangeof about 19 kilovolts per hopper may be suitably heated tomaintain theadhesive material in a liquid state so that it will flow from a.suitable opening 59 provided in thebottom of the hopper.

As the incorporated grit and adhesive material flow from the hopperon tothe 4sheet 33, "fg

g5 inch vwas maintained between them.

The mineral pulver-1aed material un one 1nstance grade. silicon carbide)was deposited When eitherof the plates is grounded, themineral streamwhich was originally at ground po-y tential is deflected toward. theungrounded plate, L

stream between 'the twoplates was attained, yet deposit of mineral wouldtake place in excess at one edge over that at another edge of the strip.g

To overcome this uneven distribution of particles, the plates may beconnected to the source of potential through a reversing switch or polelratus 96a to a source of relatively high electrical potential, 97a.

The stream of mineral at low frequencies of reversal of polarity movedfrom one plate to the other following the reversals of polarity ofelectrical potential so that over a given period of time (say oneelectrical cycle) the air space between the electrodes 92a and 03a wassubstantially uniformly filled with mineral particles.

The source of electrical energy 91a is so arranged in this circuit thatone side 98a thereof is connected'to ground.

In the case of Figure 16, the plates 92h and 93h are so arranged in thecircuitl that one of them is connected to one of the sources ofdifference of potential indicated at 91h and the other to the othersource indicated at 98h, the electrical centre of the sources indicatedat Figure 16 being grounded as at I 0B. In this arrangement aavaeos thezone whose gradient'is about 19 k. v. per inch. There is inl suchcircumstances at parently 'no tendency for the mineral particles tomigrate toward the zone of high gradient, and the general dispersion andorientation of the particles are substantially parallel, and thepotential gradient therefore substantially uniform.

Successful results may be obtained'with any of the foregoingarrangements, by the employment of an abrasive grit of a grade I ilint,preferably of a splintery nature.

We find that a higher electrical potential gradient may be maintainedwithout disruptive discharge or so-called spark-over with flint, forexample, than with other grits such as silicon carbide, inasmuch asin'the same air space potential gradient and with the same relativequantity of grit introduced thereinto, the conductivity of siliconcarbide, being higher than that of flint, tends to produce an increasedtendency to spark-over or brush discharge, as it is sometimes termed,and care must in some cases be exercised to prevent the formation of `aconducting path between the plates.

the main mineral stream becomes divided into two separate streams eachof which tended to ilow toward one of the platesthereby leaving alShould it be desired to prevent excess deposition of the grit inpredetermined areas, then the form of the invention shown in Figure 9and hereinabove described may be employed. vFor the purpose ofmanufacturing abrasive discs as disclosed herein this form of theinvention finds utility.

In Figures 17 and 17a, a further alternative arrangement of theelectrode plates is disclosed Figure 17 being a view looking down on theplates, the backing element being indicated at l0! and the plates at 92eand 93o. Figure 17a, is a view looking inwardly in the direction indi--cated by the arrow A. if In Figures 17 and 17a we disclose theelectrodes arranged in convergent planes so that some portions of thesurfaces of the discs were closer together than other portions, thepurpose being to further allow for adjustment in distribution of thegrit particles.

The grit particles entering this electrostatic eld are subjected tok avariation rin potential gradient from 17 k. v. per inch to 24 k. v. per

inch, or any other variation of the electrical A method of overcomingthis difficulty for certain purposes is shown in Figures 18 and 18a.,wherein the two plates 92d and 93d were arranged on opposite sides ofinsulating plates |02 and |03.

While the employment of these plates finds value with certain minerals,there is no marked difference in the action of the electrostatic eldwith other minerals, and we have found this stantially the same with orWithout the insulacan be regulated to a desired degree as required.

potential gradient, depending upon the voltages employed, size ofplates, etc. Y

The stream of mineral is allowed to fall into tion, but, as pointedoutin the case of some abrasive particles, an increased activity withouta resultant brush discharge was observed. The plates also serve as a'means to mechanically confine the activity of the particles to the areawithin the plates. v

Referring now more particularly to the form of the invention shown inFigure 19, it will be observed that here may be provided a form of theIapparatus wherein the electrode plates are alternately connected toground. In this form of the invention the plates indicated at |04 and|05 are connected by conductors |06 and |01 to the negative and positivesides, respectively, of sources of electrical diiierence of potential|08 and |09, that is, sources of potential beingconnected in series asshown.

A grounding switchis provided indicated generally at Illl and has itsterminals Vand I|2 thereof connected to ground as indicated at I I3,switching members H4 and I|5 serving to alternately connect theconductors |06 and |01 with ground.

It will be" seen from the form of the invention vdisclosed in Figure 19that Aby the alternative grounding of the plates |04 and |05, theorienting 'force exerted onthe particlevis uniformly mainone plate thanto the other.

" The form of the invention shown in Figure 19 operates similarly to theform of the invention shown in Figure 9. i

Reverting to the form of the invention disclosed in Figures 8 and 9, thestructure there employed including a reversal of polarity does not-include the insulating plates and these, under ordinary circumstances,are not required.

Under conditions shown in Figure 14 and without the use of insulation onthe plates or between them, flint particles dropped into the fieldwhosel so as to prevent dielectric breakdown.

The use of insulation on the plates serves to cause the mineral to bemore evenly distributed,

but it will be understood that some slight amount of orientation must besacrificed owing to the slight reduction in the potential gradientcaused by the employment of the insulating plates.

From the foregoing it 'will be observed that by adjustment of theelectrostatic iield value and/or adjustment of the plates with respectto the air space between them and/or their angularity with respect toeach other, and/or the periodicity of polarityA reversal, we are enabledto produce desired effects in the orientation and distribution of thegrit particles on the sheet.

Where the particles are deposited on shingle material for the purpose ofroofing shingles and the like, it will be observed that by causing themto lie atvon the ,adhesively coated sheets, such as an asphaltumadhesive sheet or the like, the employment of a lesser number ofparticles to cover a given area of the shingles is required.

Having thus described our invention and illustrated its use, what weclaim as new and desire to secure by LettersPatent is:

1. The process of coating an adhesively coated backing material withelongated particles with their longer axes substantially in parallelismto the backing which includes as steps thereof feeding a carrier orbacking and applying an adhesive layer to a suitable surface thereof,and depositing on'said adhesive layer a pulverulent abrasive grit ofelongated nature in respect to their major axes under the influence ofan alternating electrical eld whose lines offorce at and' adjacent tosaid carrier have an orienting effect on the particles to position themsubstantially parallel to said surface thereof.

2. Apparatus for coating adhesive. backingvicinity of said electrodes, apole changer interposed in the circuit of said electrodes, and means forguiding an adhesive coated backing adjacent to said electrodes forpositioning theA backing edgewise with respect to said electrodes. A

i of the particles (which, it will be understood, .are at groundpotential when they pass into the zone of the plates) from beingdirected more to 3. Apparatus for coating adhesive backing material withelongated particles with their longer axes substantially in parallelismto the backing surface comprising, in combination, spaced electrodesadapted to be connected to a source of alternating electrical dierenceof potential, means for feedingl an adhesive coated backing elementbetween said electrodes to guide the backing within the eldbetween saidelectrodes and to direct the backing substantially edgewise with respectto the electrodes and means for delivering abrasive particles in astream toward said backing and between said electrodes.

4. Apparatus of the character described, in combination, spacedelectrodes adapted to be connected to a source of electrical diierenceof potential, means for feeding an adhesive coated backing elementbetween said electrodes to guide the backing substantially edgewise inrespect of said electrodes, means for deliveringv abrasive particles ina stream toward said backing and between the said electrodes, and meansfor alternately grounding said electrodes.

5. 'I'he process of coating which includes as steps thereof feeding acarrier or backing and applying an adhesive layer to asuitable surfacethereof, and depositing on said adhesive layer roofing granules havingelongated dimensions under the influence of an alternating electricalfield whose lines of force at and adjacent to said carrier have anorienting effect on the granules to position them substantially parallelto said surface thereof.

6. The process of coating which includes as steps thereof feeding acarrier or backing and applying an adhesive layer to 'av suitablesurface thereof, and depositing on said adhesive layer particles offinely divided material having unequal axes under the influence of analternating electrical field whose lines of force at and adjacent tosaid carrier have an orienting effect on the particles to position themsubstantially parallel to said surface thereof.

7. In the process `of Idepositing particles of nely divided material ofelongated nature in respect of their major axes upon a surface withtheir longer axes substantially in parallelism to the surface whereinsaid particles are subjected tothe inuence of an electrical field duringtheir deposition, the step which includes reversing the polarity of saidi'leldintermittently during the deposition so as to prevent the'streamof particles from being thrown voutof the desired zone of deposition bythe action of said field.

8. Apparatus for coating adhesive backing material with elongatedparticles with their longer axes substantially in parallelism to thebacking surface comprising, in combination, spaced elecl trodes adaptedto be connected to a source of alternating electrical diierence ofpotential, said electrodes being covered with an insulating materialminimizing the formation of a conducting path between the electrodes,thereby localizing and minimizing spark-over tendencies, means forfeeding an adhesive coated backing element between said electrodes toguide the backing substantially edgewise in respect to said electrodesand means for delivering abrasive particles in a stream toward saidkbacking and between'said electrodes. RICHARD' PAUL CARLTON.

THEODORE JOSEPH MILLER.

